TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination
Benjamin C. Chandler, Leah Moubadder, Cassandra L. Ritter, Meilan Liu, Meleah Cameron, Kari Wilder-Romans, Amanda Zhang, Andrea M. Pesch, Anna R. Michmerhuizen, Nicole Hirsh, Marlie Androsiglio, Tanner Ward, Eric Olsen, Yashar S. Niknafs, Sofia Merajver, Dafydd G. Thomas, Powel H. Brown, Theodore S. Lawrence, Shyam Nyati, Lori J. Pierce, Arul Chinnaiyan, Corey Speers
Benjamin C. Chandler, Leah Moubadder, Cassandra L. Ritter, Meilan Liu, Meleah Cameron, Kari Wilder-Romans, Amanda Zhang, Andrea M. Pesch, Anna R. Michmerhuizen, Nicole Hirsh, Marlie Androsiglio, Tanner Ward, Eric Olsen, Yashar S. Niknafs, Sofia Merajver, Dafydd G. Thomas, Powel H. Brown, Theodore S. Lawrence, Shyam Nyati, Lori J. Pierce, Arul Chinnaiyan, Corey Speers
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Research Article Oncology

TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination

Abstract

Increased rates of locoregional recurrence are observed in patients with basal-like breast cancer (BC) despite the use of radiation therapy (RT); therefore, approaches that result in radiosensitization of basal-like BC are critically needed. Using patients’ tumor gene expression data from 4 independent data sets, we correlated gene expression with recurrence to find genes significantly correlated with early recurrence after RT. The highest-ranked gene, TTK, was most highly expressed in basal-like BC across multiple data sets. Inhibition of TTK by both genetic and pharmacologic methods enhanced radiosensitivity in multiple basal-like cell lines. Radiosensitivity was mediated, at least in part, through persistent DNA damage after treatment with TTK inhibition and RT. Inhibition of TTK impaired homologous recombination (HR) and repair efficiency, but not nonhomologous end-joining, and decreased the formation of Rad51 foci. Reintroduction of wild-type TTK rescued both radioresistance and HR repair efficiency after TTK knockdown; however, reintroduction of kinase-dead TTK did not. In vivo, TTK inhibition combined with RT led to a significant decrease in tumor growth in both heterotopic and orthotopic, including patient-derived xenograft, BC models. These data support the rationale for clinical development of TTK inhibition as a radiosensitizing strategy for patients with basal-like BC, and efforts toward this end are currently underway.

Authors

Benjamin C. Chandler, Leah Moubadder, Cassandra L. Ritter, Meilan Liu, Meleah Cameron, Kari Wilder-Romans, Amanda Zhang, Andrea M. Pesch, Anna R. Michmerhuizen, Nicole Hirsh, Marlie Androsiglio, Tanner Ward, Eric Olsen, Yashar S. Niknafs, Sofia Merajver, Dafydd G. Thomas, Powel H. Brown, Theodore S. Lawrence, Shyam Nyati, Lori J. Pierce, Arul Chinnaiyan, Corey Speers

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Figure 2

Inhibition of TTK confers radiosensitivity in multiple basal-like BC cell lines with high baseline TTK expression.

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Inhibition of TTK confers radiosensitivity in multiple basal-like BC cel...
(A and C) shRNA-induced TTK knockdown (shTTK) increased radiosensitivity in MDA-MB-231 (rER: 1.21–1.63) and BT-549 (rER: 1.21–1.26) cell lines. (B and D) The addition of Dox led to TTK knockdown in multiple stable clones in MDA-MB-231 and BT-549 cell lines. (E–G) Pharmacological inhibition of TTK induced radiosensitivity of MDA-MB-231 cells (rER: 25 nM 1.15–1.18, 37.5 nM 1.23–1.29, 50 nM 1.34–1.39), BT-549 cells (rER: 25 nM 1.10–1.17, 37.5 nM 1.11–1.30, 50 nM 1.23–1.39), and SUM-159 cells (rER: 25 nM 1.11–1.26, 37.5 nM 1.35–1.64, 50 nM 1.74–2.27) in a dose-dependent fashion. Data represent the mean of 3 independent experiments, and error bars represent SEM for clonogenic assays and SD for SF-2 Gy. A 2-sided Student’s t test was used for comparison of shRNA clonogenic assays, and a 1-way ANOVA with Dunnett’s multiple comparisons test was used for comparison of B909 clonogenic assays. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. shCon, shControl.